Until recently the Diplock courts only tried Republican or Loyalist paramilitaries. In the first case in which a person not associated with the Troubles was tried and convicted, Abbas Boutrab, a suspected al-Qaeda sympathiser, was found guilty of having information that could assist bombing an airliner.[6] A sentence of six years was handed down on 20 December 2005.[7]

Diplock courts were common in Northern Ireland for crimes connected to terrorism.[8] The number of cases heard in Diplock courts reached a peak of 329 yearly in the mid-1980s. With the Northern Ireland peace process that figure fell to 60 a year in the mid-2000s.[9] On 1 August 2005, the Northern Ireland Office announced that the Diplock courts were to be phased out, and in August 2006 they announced that the courts were to be abolished effective July 2007. This was achieved under the Justice and Security (Northern Ireland) Act 2007.

Non-jury trials, however, may still be used in Northern Ireland, as elsewhere in the UK, but only in exceptional cases.[8][10]

The transition from internment to Diplock Courts was the culmination of a series of proposals put forth by Brigadier Frank Kitson. Kitson's work appeared to be a blend of sociological 'normalisation', political policy and legal plasticity. In Kitson's book on counter-insurgency published in 1970, he advocated for the Courts to be used as another part of the Army's arsenal in the fight against insurgents. He argued:

…the Law should be used as just another weapon in the government’s arsenal, and in this case it becomes little more than a propaganda cover for the disposal of unwanted members of the public. For this to happen efficiently, the activities of the legal services have to be tied into the war effort in as discreet a way as possible...[11]

On the other hand, the establishment of the Diplock Courts can be seen as an early, and successful, example of PIRA's long-term aim of making 'the Six Counties... ungovernable except by colonial military rule'. This was one of the central pillars of the 'Long War' strategy set out in the 1977 'Green Book':[12] while PIRA claimed its armed struggle sought to end British 'colonial' rule, its leadership realised that Catholic perception of British 'colonialism', and the subsequent disillusionment caused by this, was of great value in persuading the Catholic community to embrace the Republican cause.

In his report, Lord Diplock, cited two primary reasons for his determination that jury trials should be suspended, 1) danger of perverse acquittals, and, 2) jurors had been threatened, "of which we have had ample evidence".[13] Two years later Lord Gardiner's review of the removal of trial by jury, included attempts to bolster Diplock's findings as follows:

We are convinced on the evidence that we have received, that if juries were to be reintroduced for scheduled offences, their verdicts would still be subject to the influences of intimidation, or the fear of it. We have no evidence of this or of perversity in juries...[14]

The Gardiner Report found that “no evidence” existed on which the removal of the jury was based but concluded that non-jury trials should continue.

^Greer & White: Abolishing The Diplock Courts, page 91: Report of a Committee to consider, in the context of civil liberties and human rights, measures to deal with terrorism in Northern Ireland, Lord Gardener.

^Donohue, Laura (2007): Counter Terrorist Law and Emergency Powers in the United Kingdom 1922–2000, S. 155